Initialism of management information system.
"The intelligence officers gathered in the secure room to debrief about their recent operations as members of the MIS."
plural of MI
In plain English: Mis is an old-fashioned word for a mistake or error that someone makes.
"The judge ruled that there was no mis in the case because the evidence was clear."
Initialism of Military Intelligence Service (United States).
"The acronym MIS in that context stands for Military Intelligence Service, a United States organization formed during World War II."
The English word "mis" likely comes from several different sources rather than one single origin. It may have been borrowed as a nickname meaning "bear" or "mouse," derived from Polish, Slovene, or Dutch names, or it could come from the surname Mis found in Yucatán Maya culture.